1. Field of the Invention
The present invention relates generally to a computer system with a display device, such as a cathode ray tube (CRT) or liquid crystal display (LCD), for example. The display device provides a user of the computer system with a visible display of computer data, such as text or graphics. More particularly, the present invention is in the field of such a computer system having a Video Display Controller (VDC) including a graphics generator. The VDC receives image information, such as text or graphics generated by a processor (CPU) or retrieved by the CPU from another facility (such as a CD-ROM) of the computer system, and provides signals driving the CRT or LCD display. The computer system may be a battery-powered portable device. Still more particularly, the present invention is in the field of a VDC having a power saving mode for responding to both hardware inputs (such as a contact closure input, for example) and also to a software input to effect a reduction in power consumption within the VDC and the computer system as a whole.
2. Related Technology
A conventional power manager for a portable laptop computer is known in accord with U.S. Pat. No. 5,167,024 (hereinafter, the '024 patent), issued 24 Nov. 1992 to R. Steven Smith, et. al. According to the '024 patent, a power manager for a laptop computer provides power management and clocking control to various units of the computer. Switches control the distribution of power to the various units of the computer. When any of these various units are not needed, the switches are used to remove power or clock signals, or both, from particular units of the computer. The power manager allows the computer to be in any one of four states varying from "on" and active, to "on" in a "sleep" state with power and/or clock signals removed from certain units, to "on" in an "intermediate" or "slow" state in which the clock rate of the computer is reduced to result in a power saving. The fourth state for the computer system is "off".
With a power manager as disclosed in the '024 patent, a system designer is limited to three functional modes for the computer, only two of which are modes with reduced power consumption. Further, the system criteria which will initiate one of the two modes of reduced power consumption are relatively limited.
Another conventional real-time power conservation apparatus for portable computers in known in accord with U.S. Pat. No. 5,218,704 (hereinafter, the '704 patent), issued 8 Jun. 1993 to LaVaughn F. Watts, Jr., et.al. According to the '704 patent, a real-time power conservation apparatus for a portable computer employs a monitor to determine whether a computer may rest based upon CPU activity. A hardware device carries out the result of the monitor's determination. Again, with this conventional power conservation apparatus, the system designer options as to how power conservation expedients are to be implemented are limited.
Yet another conventional power management system for a battery-operated computer is known in accord with U.S. Pat. No. 5,230,074 (hereinafter, the '074 patent), issued 20 Jul. 1993, to Francis J Canova, Jr., et.al. According to the '074 patent, a battery-operated computer includes two processors, a main processor, and a processor which manages power receipt (battery charging) and power usage within the computer. The system designer using the power management system taught by the '074 patent would be constrained to configure the power management options of a computer system according to the choices allowed by the teaching of this patent.
Two more recent conventional power saving or power conservation apparatus are known in accord with U.S. Pat. Nos. 5,369,711; and 5,396,635, issued 29 Nov. 1994, and 7 Mar. 1995, respectively, to Steven J. Gettel, and Henry T. Fung, also respectively. These teachings both employ software routines to control a monitor for determining which of available power conservation or power saving expedients are to be implemented. A user of either one of these power saving expedients will be required to select from among a limited field of power saving configurations for each mode of operation of the computer system. Also, implementation of these power saving apparatus is rather complex, requiring use of separate power management IC.
Accordingly, a long-felt need has been recognized in the field of battery-operated portable computers for such a computer system which has both a high level of graphics generating capabilities and an economy of operation effected by a power saving facility of the VDC of the computer system which results in a comparatively long battery-powered service life between battery recharging.